I made this indicator specifically for my circle jig, but as long as the center-pin is 5mm it will fit any other as well.

I got tired of not being able to properly measure the radius on my circle cutter, also the endless calculations (like subtracting half the width of the pin etc), so I decided to make a little indicator that helps me with that.

You just set your desired radius, put it on top of the pin and set the circle jig accordingly. No calculating: the endstop for a ruler is on the center of the center-pin, and the indicator on the sled in line with its endstop. You can either place a slim ruler (like shown above) or glue a paper-ruler like from Ikea or a home-imrpovement-store to it; however a paper ruler would have to have the markings on the right side (when 0 is on the top and growing numbers go bottom), so not like the ruler I have in the picture :) also make sure that the markings are actually accurate. The curve on the sled has a diameter of 17mm, this will fit even large bits like my 16mm Bosch and most bearings as well.

You can also turn the sled 180° to measure for an inside-radius. Max radius is around 154mm

You also need an M3 screw with hex-head, 25mm length, as well as a wingnut of some sort. Or you can use an M3 nut and a thumbscrew of 25mm - that one will need some trimming though.

I am aware that the provided printing profile seems a bit stupid with all the support. But only in this orientation, the endstop can be printed with a really sharp corner. Without that, your measurements can easily be off.